Dispersants for a hydraulic composition are chemical admixtures, and used for dispersing cement particles, thereby reducing a unit water quantity necessary for achieving a required slump and enhancing workability and the like of a hydraulic composition. Examples of conventionally-known dispersants include naphthalene-based dispersants such as a formaldehyde naphthalenesulfonate condensate, polycarboxylic acid-based dispersants such as a copolymer of a carboxylic acid and a monomer having an alkylene glycol chain, and melamine-based dispersants such as a melaminesulfonic acid-formaldehyde condensate.
Compared to polycarboxylic acid-based dispersants, naphthalene-based dispersants are characterized in that they have smaller fluctuations in exhibiting the fluidity in response to changes of materials or temperatures, and a hydraulic composition obtained thereby has a relatively low viscosity and they are easy to use in manufacturing a hydraulic composition.
Meanwhile, compared to naphthalene-based dispersants, polycarboxylic acid-based dispersants are characterized in that they can exhibit a good dispersibility to a hydraulic composition having a relatively low water/cement ratio. However, as regarded as a drawback in JP-A 2003-321264, JP-A 2007-210877 and JP-A 2011-207669, the effects of polycarboxylic acid-based dispersants are exhibited in a temperature dependent manner, and the effects such as the fluidity and the material separation resistance are likely to change under high temperature such as the summer season and under low temperature such as the winter season.
JP-A 2003-321264 discloses a hydraulic composition containing a polycarboxylic acid-based water reducing agent, cement and a metal salt of a specific carboxylic acid monomer.
JP-A 2007-210877 discloses a dispersant for a hydraulic composition, which contains a specific polycarboxylic acid-based polymer and a polymer having a specific phosphate group.
JP-A 2011-207669 discloses a hydraulic composition, which contains a hydraulic component, an inorganic impalpable powder, and a specific modified polycarboxylic acid-based fluidizing agent.
It is considered that when a naphthalene-based dispersant and a polycarboxylic acid-based dispersant are used in combination, the drawback on the temperature dependency is overcome while good dispersibility is exhibited to a hydraulic composition having a relatively low water/cement ratio. However, in actuality, as described in JP-A 2006-169078 and JP-A 2006-168305, combined use of a naphthalene-based dispersant and a polycarboxylic acid-based dispersant reduced the fluidity of a hydraulic composition, and a dispersant satisfying a practically usable level could not be obtained.
JP-A 2006-169078 discloses a water reducing agent for cement, which contains a polycarboxylic acid compound having 3 or more carboxyl groups per one molecule, a naphthalene sulfonic acid-based water reducing agent and a soluble acid calcium salt having a water solubility of 5 or more (at 25° C.).
JP-A 2006-168305 discloses a method for adding a water reducing agent for cement, which includes: kneading, with water, a hydraulic composition containing a polycarboxylic acid compound having 3 or more carboxyl groups per one molecule, an acid alkali metal salt, a calcium salt of which is water soluble, and cement; and then adding a sulfonic acid-based water reducing agent.